Seahawks dominate from the start in 42-13 victory, the largest margin of defeat for 49ers since Jim Harbaugh became head coach

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Seattle's Richard Sherman intercepts a pass thrown into the end zone by Colin Kaepernick. (Photo by Otto Greule Jr/Getty Images)

Last week’s 49ers victory was a classic.

Sunday night, the Niners suffered a classic beatdown.

The Seahawks crushed San Francisco 42-13, the largest margin of defeat since Jim Harbaugh became head coach. The Seattle victory opens the door to possibly wrestling the NFC West title away from the 49ers next week.

Now, the 10-4-1 49ers must hope to beat the Arizona Cardinals this coming Sunday afternoon at Candlestick Park to stave off the Seahawks, who with Sunday night’s victory improved to 10-5 and secured a playoff spot. The loss Sunday night also means the Niners’ chances of securing a first-round bye are more difficult.

For the 49ers – who looked so good in a victory over the Patriots last Sunday night – an encore on the prime-time stage was ugly almost from the beginning.

San Francisco received the opening kickoff, but went three-and-out, and the Seahawks immediately responded with a touchdown on their second play from scrimmage.

Playing in front of their loud home crowd, the Seahawks dominated the lines of scrimmage, ran the ball almost at will with Marshawn Lynch (who rushed for 111 yards) and played a physical, opportunistic style that put the Niners in a quick, deep hole from which they never were able to escape.

Lynch scored his second touchdown on Seattle’s next possession to put the Seahawks up 14-0. Then came perhaps the biggest play of the game.

After the 49ers marched to the Seattle 3-yard line early in the second quarter, David Akers came out for a short field goal attempt that would have cut the deficit to 14-3. Instead, defensive lineman Red Bryant, surging through the middle of the line, reached up to block the kick. The ball bounced to Richard Sherman, who raced 90 yards for a TD to put Seattle up 21-0.

By halftime, the Niners trailed 28-6 and never were able to rebound in the second half of a rainy night in the Pacific Northwest.

For the Seahawks, the victory avenged a 13-6 loss to the Niners in San Francisco earlier this season and keeps one of the NFL’s hottest teams on a roll. According to Elias, the Seahawks now have scored 150 points in their past three games; the only team with more over a similar span was the 1950 Rams, who scored 165. Seattle is now 7-0 at home this season.

Not only did the Niners lose, but they lost tight end Vernon Davis early in the game to a concussion on a hit by Seattle safety Kam Chancellor. San Francisco also had to play without All-Pro defensive lineman Justin Smith, who suffered an elbow injury in last Sunday night’s victory over the Patriots.

Niners QB Colin Kaepernick finished the night 19-of-36 for 244 yards, but threw one interception in the end zone and was often off target much of the night. The Seattle defense also put the clamps on the running game, which netted just 82 yards. Frank Gore was held to 28 yards on six carries.